3-Hydroxypropanal is an intermediate product in the preparation of 1,3-propane diol. 1,3-Propane diol may be further processed to form polyesters, for example poly(trimethylene terephthalate), which is useful for the spinning of fibers, or may be processed to other articles of commerce such as polyols.
It is known that 3-hydroxypropionaldehyde (3-hydroxypropanal) can be prepared by hydration of acrolein with water in the presence of a chelate-forming ion exchanger at temperatures of 30 to 120.degree. C. and pressures of 1 to 20 bars as described in U.S. Pat. No. 5,171,898, herein incorporated by reference.
U.S. Pat. No. 5,284,979 discloses the hydration of 2-alkenals to 3-hydroxyalkanals in a homogeneous phase in the presence of an acid catalyst and a dissolved acid-base buffer which results in a pH of from 2 to 5. A preferred acid base buffer is propanoic acid/triethyl ammonium propionate.
EP 0713853 discloses the addition of oxalic acid to a process for the hydration of acrolein to 3-hydroxypropanal in the presence of a lead-containing ion exchange resin.
Japanese Patent application Kokai No. H 8-143502 discloses the preparation of 3-hydroxyalkanals by the hydration of unsaturated aldehydes in the presence of a metal-carrying ion-exchange resin with the addition of a carboxylic acid to the reaction mixture. Mono and polycarboxylic acids are broadly disclosed, a dicarboxylic acid such as oxalic acid is especially preferred.
The known processes have the disadvantage that the catalysts used do not exhibit life times as long as desired. Life time is impaired because of depositions of acrolein polymers on the ion exchanger bed occurring over the course of operation. The acrolein polymers create an increase in pressure differential across the ion exchanger bed and hence a drop in conversion of the unsaturated aldehyde. The ion exchanger must, therefore, be renewed periodically after undesirably short periods of time.
Achievement of economic continuous operation, however, requires an adequately long life time. An object of this invention, therefore, is to improve the known process for the preparation of 3-hydroxypropanal by providing adequately long catalyst life times.